Charging antimony-free VRLA batteries without float

[HiTech]

Here is a proposed much lower float current method to charge non-antimony batteries. Supposedly better than traditional float.

Low current float for AGM

[full_mosey]

Hi Jim;

As a hobby or test case I can understand your curiosity about your AGMs. Thanks for posting your details as the info is beneficial to any interested parties, including myself.

An AGM is pressurized. I do believe there is capacity loss in the same manner that a tire loses pressure simply by the movement of atoms. I believe that is baked into the design. However, to deliberately walk a high voltage tightwire that could possibly lose gas, means a loss of H and O that is not baked into the design, is asking for trouble. I trust my two MS PWM controllers, with temp comp, to work unattended every day.

If the valves are intact, it should be nearly impossible to reintroduce H2O because AGMs are watertight submerged to 30ft. Another plus in a marine use if there is a concern for Chlorine gas.

If the valves are broken, then you really don't have a proper AGM battery. Yes it has a-g-m but the chemistry is not to spec.

HTH;
John

[HiTech]

Trying to find the routine for max battery life.

When bringing the AGMs into service my research showed that all strings vent a little from the stronger cells for the first few weeks. When I reconditioned my car AGM which ran flat, the procedure was actually designed to create bubbling and a small amount of venting.

I devised a simple way to find with each battery if there was any gassing going on by routing the vent hose into water or floating a ring of distilled (in case it were ingested) water on top. Based on watching these, and based on following manufacturer recommended charging protocol with various different chargers, it is my belief that AGMs vent a *little* (at a level you cannot hear or smell) far more than their owners may realize.

For example after our power outage, the first real use of the AGMs in production (I've still yet to load test them - need better short cables for the big inverter), I thought they were charged back to full. But this is tricky. I have found if they are really full they will have a voltage of 12.93v after 24 hours. They were only at 12.87.

I noticed the smart charger (I know, I know!) floats other batteries within a few hundredths of the manufacturer recommended float and temp was within a few degrees of 77, so I gave it a try. After not too long I saw a bubble, then a few minutes later one from another cell.

Because I do not leave them full time on float but top them off at least once a week, it is possible the string has not fully gone though it's initial equalization (supposed to take weeks under full time float) after which that initial minimal outgassing is supposed to stop.

SO I decidedly want to stay away from any venting (the bubble is not a bubble in free electrolyte, but it is still gas that escaped the regulation valve and was not recombined internally to electrolyte in the battery). The reconditioned AGM did make some bubbling noises as part of the reconditioning procedure. ABsolutely that dried out the AGM some but it restored capacity compared to a badly sulphated AGM that it was.

My desire here is to be able to really float indefinately, without any undected venting taking place. I think to really do that I am going to need a temperature compensated float charger.

Looking at the paper it was interesting to see what happens to a battery between no charging and an upper bound of float charging. I don't trust any charger I have yet to leave on the battery 24x7. Cranking something slightly to the low side is interesting to me - not sure if that or the daily cycles of solar would do the battery more good (since the battery sits not charging all night every night and does a tiny shallow cycle every day due to tiny self discharge).

Really it is more for my learning than anything else. But getting my little string on a near telecom grade of standby charge since it's usage is very much more like standby service than cycling service is just a bit of a hobby at the moment.

Jim

[full_mosey]

HiTech wrote:
I have been floating mine to manufacturer spec when temp is close to 77, and using the PWM solar controller tweaked to the recommended charge voltages (on battery temp compensated) the rest of the time.

So far so good. I only see outgassing (like a bubble a minute) if the temp climbs above 90 and the battery is on float.

I guess my biggest takeaway from this paper is running say a tenth of a volt under temp compensated ideal float may not be the end of the world. My own experience is that a tenth over on AGMs could potentially be slowly destructive.

Every bubble causes me pain lol.

Jim

Is this an OCD in trying to stay on the highest voltage tightwire? If so, why? What are the expected improvements?

I would be very concerned if my AGMs were bubbling at all. Do you mean to say you are exceeding the valve pressure and releasing gas?

IMHO, every bubble that escapes translates into lost capacity. That is a no-go for me.

A proper temp compensating charger should prevent any gassing at the plates. If plates are bubbling, does charging take place under the bubbles? Is gassing really needed with AGMs, after all, there is no need to stir? What good can come from any bubbling?

HTH;
John

[MEXICOWANDERER]

It goes beyond mere adherence to a given constant voltage.

The PERCENTAGE of kWh consumed in float mode over a given period of time is the key fundamental that must be implemented. If a pure Pb or calcium calcium cell has been calculated to lose 1.06% A/H capacity 30 days and you discover 2.95% being delivered...it's time to find out why. This absolutely can not be done by voltage control only.

The key word is FLOAT. Maintenance.

[pianotuna]

Hi Jim,

I do not have the luxury of 24 hour shore power charging. I feel that a sophisticated solar controller with temperature compensation is the "way to go". Put one between the charger and the battery bank. The controller won't care that the energy is coming from shore power instead of from a solar source.

-or-

Do as I mostly do and let the solar system meet the needs of the battery bank. Self discharge rates on agm format are extremely low.

[HiTech]

I have been floating mine to manufacturer spec when temp is close to 77, and using the PWM solar controller tweaked to the recommended charge voltages (on battery temp compensated) the rest of the time.

So far so good. I only see outgassing (like a bubble a minute) if the temp climbs above 90 and the battery is on float.

I guess my biggest takeaway from this paper is running say a tenth of a volt under temp compensated ideal float may not be the end of the world. My own experience is that a tenth over on AGMs could potentially be slowly destructive.

Every bubble causes me pain lol.

Jim

[MEXICOWANDERER]

Be EVER so careful interpreting an exercise such as this into real world practicality.

The mere evolution of 1% calcium added to the negative plate (i.e. hybridization)can skew all of the data beyond uselessness.

I do not care for this paper. Complete qualifications need to be prefixed, suffixed and annotated to the text. First up, what is/was the construction methodology of the units under test? Plate thickness? Plate paste? I did not even get so far as to read if the electrolyte was absorbed, or gelled. Some VRB's use liquid electrolyte. What was the density of the electrolyte? Variances per pack after test?

There are innumerable methods to determine inappropriateness of battery maintenance voltage amplitude.

The article mentions early failure of VRB used for standby. It does not mention the sloppiness, variance from design specification found in apparatus chargers.

For crying out loud 99% of the VRB maintenance chargers out there have zero temperature compensation.

There exists a formula expressed in kWh / ampere hours capacity used to determine the amount of energy needed to maintain a lead acid battery. Yes it must be emended for temperature.

[HiTech]

I am looking not to cook my AGMs. For a while I was thinking 24x7 float was the best thing for them while in storage. I am rethinking that. Maybe what the PWM does is fine.

Float is a very specific temp corrected voltage that leads to a certain current level. This is a charge rate below that. I guess below float might be more accurate.

I devised a way to watch for outgassing on my AGMs and they will evolve hydrogen and oxygen much more easily than many people think. A little does not hurt, but much dries out the battery...forever reducing capacity. I am looking for that tightrope between sulfation and outgassing.

Jim

[MNtundraRet]

The test procedure was interesting, but you title was misleading.

Your title stated charging "without float". The test is "low float".

Also; the article is for a proposed better method to charge batteries used to power emergency lights, critical computers, etc., when 120v, ac, power is lost.

These batteries spent 95% of their life being "float charged" until the time comes that they actually get used. Because of this the battery life end up short for batteries rarely getting used.

I fail to see how this could help any of us for RV use, unless the RV has been stored for a long winter (like the current). My 9-watt, 0.625 amp, solar panel accomplishes this goal for me each long winter.

In your case you get out much more often and need to recover to "full" charge much more often. I guess what it really means is that if your batteries were really "fully" charged, if you could manually lower your float charge to the very low "float" it MIGHT help in the long run. Not an easy job since you need to know the discharge rate of each battery being stored to calculate the lower "float" rate.

Mark B

[pianotuna]

Hi Jim,

Great article thanks for posting it.